First off, am i dealing with fungus?I believe so, but since i've never seen it before it would be nice for someone else to confirm it for me.

The lens is a Canon EF 75-300 4-5.6 - the lens-barrel says ultrasonic, but nothing about usm in the name.

I've been staring at it for quite some time now, and i think i've managed to locate which part of the lens the fungus is sitting on. The second glass element from the rear. Can i access and clean this part of the lens without destroying it?My biggest worry is that accessing this part of the lens will put something out of alignment? I don't know anything about lens manufacturing and repairing, so this might be very wrong.

Now, i'm somewhat confident in my fiddling abilities, but i'd like to make sure i do not missalign anything rendering the lens useless. My plan is:Leave it in direct sunlight, to kill the possible fungus for good.Access and clean the infested element. Doing the cleaning with 93% alcohol, yes?Seal my new toy up and keep it stored in better conditions.

Some of you will probably tell me that this lens isn't worth spending my time on, but my non-existing budget is smaller than small and i'd really like to play around with the reach this lens provides.

It does look like fungus to me. There is a paranoia aspect here, which is could it spread to other currently good lenses? If it is early enough, you might get away with cleaning, but apparently they can damage the lens surface too.

If its still in Warranty, Id rather just walk up to Canon HQ in your area and get them to clean it. If its not in warranty, Id still get them to take a look at it - they didnt charge me when I got them to look at a lens, but they said it would cost such and such to fix and I had a choice to go ahead.

So Canon will tell you b4 they charge you if its worth cleaning or if it is in fact fungus and tell you how much it will cost you to fix.

With me, I had a stiff zoom ring and they just said what it was, it would cost so much and I went ahead of it.

I understand this, my main concern is whether i can put something out of alignment by simply accessing and cleaning the element i want. I've tried googling, without luck though, so i was hoping that someone could enlighten me here.

popo wrote:

It does look like fungus to me. There is a paranoia aspect here, which is could it spread to other currently good lenses? If it is early enough, you might get away with cleaning, but apparently they can damage the lens surface too.

I worried about this when i found the possible fungus and kept the lens away from other equipment. I've been googling abit and as far as i understand spreading isn't really a threat. The spores needed to grow this fungus-business is everywhere, it is a matter of exposing the lens to the right(wrong) conditions. What looked liked fungus spreading was explained as presenting both lenses to fungus-friendly environments and simply having two different fungus-families growing in each lens.

My own 'experience' sort of supports this. The lens with fungus have been kept together with another lens and camera for quite some years, without any 'spreading'. My own sherlock homes guess is that the infested lens caught some fungus in some humid conditions and was then moved to its current dry place, where the plants died and nothing more happened.

I'll have a look for the sources on this, but i'm not sure i can dig that up. I hope this makes any sense, i'm a bit confused myself.